It is hypothesized that the quantity of coronary artery calcification is significantly associated with biochemical and genetic factors, such as elevated Lp (a) and the presence of the apoE4 allele, which have been linked epidemiologically to premature coronary heart disease. The specific aims are, to use electron beam CT (EBCT) to quantitate coronary artery clacification (CAC) in siblings with family histories of premature coronary disease and use sib pair analysis to determine the association of CAC with several biochemical and genetic factors such as Lp (a) and apoE4.